The Study Of Stroboscopic Effect In AC LEDs

With the rapid development of solid-state lighting technology, LED is widely used in lighting engineering with its advantage of energy saving, environmental protection and high luminous efficiency. Traditional LEDs is a DC LED light source, it must be equipped with AC/DC and constant current source which not only increases the cost of the light source, also causes a waste of energy and limits the LED’s lifetime. AC LEDs can directly drived by AC power, and it gradually becomes a new trend in the lighting industry because of low cost, small size and high conversion efficiency. However, AC LEDs can easily cause the stroboscopic phenomenon due to its intensity changing over time. The stroboscopic effect is a crucial factor in lighting quality. It not only affects people’s visual comfort, also can induce physical diseases such as migraine. Therefore, this paper is dedicated in researching the stroboscopic effect of AC LEDsThe visibility and acceptability of stroboscopic effect were investigated using the psychological evaluation methods based on LEDs which driving wave can be controlled.Firstly, the effects of driving waves on stroboscopic visible threshold were studied in this thesis. The results show that there is a proportional relationship between square wave and sine wave in visibility of stroboscopic effect; with the increase of frequency, the stroboscopic effect threshold of sine wave increases; the illuminance of of the light source has a significant effect on stroboscopic effect visibility. For the indoor lighting condition, with the increase of intensity of illumination, stroboscopic effect visible threshold showed a trend of U shape, the most obvious illuminance rangees from 10 to 100 lux. For the outdoor lighting condition, with the increase of intensity of illumination, stroboscopic effect visible is becoming small until stable.Secondly, the stroboscopic visibility measurement model is verified using the complex waves. The results show that the visibility measurement model can accurately predict the stroboscopic visibility.Finally, the acceptability of stroboscopic effect was studied in thesis. The results indicate that modulation depth has significant effect on acceptability. The feeling of "Fliker" and "Motion artifacts" becomes annoying with increasing modulation depth. The acceptability of stroboscopic effect is 75% modulation depth, and the visibility threshold is 17.4% under the IOOHz 50% duty cycle square wave lighting condition. We can see that the acceptability of stroboscopic effect is much larger than the visibility value.